1. Field of the Invention
This invention relates to an automatic transmission system for use with automobiles, and more particularly, an automatic transmission system to control automatically the operation of a transmission gear in relation to the operational conditions of an automobile, including its running as well as parking condition. Transmission include a gear wheel system and an engaging means to make the gear wheels engage selectively with one another.
2. Description of the Prior Art
In the conventional automatic automobile transmission systems, the engaging means is generally operated by hydraulic pressure to effect the changing-over operations of the transmission system. However, such hydraulic systems make the whole control system complicated and are unable to give a transmission system an advantageous optimum operating condition. To solve the aforementioned problem, it has been proposed to employ a combination of electric and hydraulic systems, as disclosed in Japanese Patent Publication Nos. 36284/72, 210/73 and 211/73. In such a system, the hydraulic system is made simpler but still requires mechanical linkage to set the forward, reverse, parking and nutral transmission positions. The linkage operates manual valves provided in the control system of the transmission and requires relatively high accuracy for its positioning. However, since the transmission inevitably changes its relative position in the body during the running of the automobile, a linkage which allows for a relative movement between the body and the transmission is necessary. Said linkage must also provide precise movement and is complicated and difficult to design. Furthermore, when this type of transmission is mounted in a different type of body, the design of the linkage must be altered to suit the body. Moreover, since the parking brake provided in the conventional automatic transmission system is of a manual type operable with a mechanical linkage, it is also bound with the aforementioned drawbacks and, in addition, it is difficult to release the parking brake when the automobile is parked on a steep slope because a large force is required to manipulate the handle and release the brake. Furthermore, since it can be said that some drivers fail to shift the gear lever into the parking position when parking the automobile, there is always the danger that the automobile might inadvertently start to move by itself.